1. Field of the Invention
The present invention relates to a heat-assisted magnetic recording head for use in heat-assisted magnetic recording where a recording medium is irradiated with near-field light to lower the coercivity of the recording medium for data recording.
2. Description of the Related Art
Recently, magnetic recording devices such as a magnetic disk drive have been improved in recording density, and thin-film magnetic heads and magnetic recording media of improved performance have been demanded accordingly. Among the thin-film magnetic heads, a composite thin-film magnetic head has been used widely. The composite thin-film magnetic head has such a structure that a reproducing head including a magnetoresistive element (hereinafter, also referred to as MR element) for reading and a recording head including an induction-type electromagnetic transducer for writing are stacked on a substrate. In a magnetic disk drive, the thin-film magnetic head is provided in a slider which flies slightly above the surface of the magnetic recording medium.
To increase the recording density of a magnetic recording device, it is effective to make the magnetic fine particles of the recording medium smaller. Making the magnetic fine particles smaller, however, causes the problem that the magnetic fine particles drop in the thermal stability of magnetization. To solve this problem, it is effective to increase the anisotropic energy of the magnetic fine particles. However, increasing the anisotropic energy of the magnetic fine particles leads to an increase in coercivity of the recording medium, and this makes it difficult to perform data recording with existing magnetic heads.
To solve the foregoing problems, there has been proposed a technique so-called heat-assisted magnetic recording. This technique uses a recording medium having high coercivity. When recording data, a magnetic field and heat are simultaneously applied to the area of the recording medium where to record data, so that the area rises in temperature and drops in coercivity for data recording. The area where data is recorded subsequently falls in temperature and rises in coercivity to increase the thermal stability of magnetization.
In heat-assisted magnetic recording, near-field light is typically used as a means for applying heat to the recording medium. A known method for generating near-field light is to irradiate a plasmon antenna, which is a small piece of metal, with laser light. The plasmon antenna has a near-field light generating part which is a sharp-pointed part for generating near-field light. The laser light applied to the plasmon antenna excites surface plasmons on the plasmon antenna. The surface plasmons propagate to the near-field light generating part of the plasmon antenna, and the near-field light generating part generates near-field light based on the surface plasmons. The near-field light generated by the plasmon antenna exists only within an area smaller than the diffraction limit of light. Irradiating the recording medium with the near-field light makes it possible to heat only a small area of the recording medium.
In general, the laser light to be used for generating the near-field light is guided through a waveguide that is provided in the slider to the plasmon antenna that is located near the medium facing surface of the slider. Possible techniques of placement of a light source that emits the laser light are broadly classified into the following two. A first technique is to place the light source away from the slider. A second technique is to fix the light source to the slider.
The first technique is described in U.S. Patent Application Publication No. 2006/0233062 A1, for example. The second technique is described in U.S. Patent Application Publication No. 2008/0055762 A1 and U.S. Patent Application Publication No. 2008/0002298 A1, for example.
The first technique requires an optical path of extended length including such optical elements as a mirror, lens, and optical fiber in order to guide the light from the light source to the waveguide. This causes the problem of increasing energy loss of the light in the path. The second technique is free from the foregoing problem since the optical path for guiding the light from the light source to the waveguide is short.
The second technique, however, has the following problem. Hereinafter, the problem that can occur with the second technique will be described in detail. The second technique typically uses a laser diode as the light source. Laser light emitted from the laser diode can be made incident on the waveguide by a technique described in U.S. Patent Application Publication No. 2008/0055762 A1, for example. This publication describes arranging the laser diode with its emission part opposed to the incident end of the waveguide so that the laser light emitted from the emission part is incident on the incident end of the waveguide without the intervention of any optical element. According to this technique, the laser diode is arranged so that the longitudinal direction of the laser diode, i.e., the direction of the optical axis of the laser light to be emitted from the emission part, is perpendicular to the end face of the slider where the incident end of the waveguide is located. In such a case, the laser diode needs to be positioned with high precision so that the optical axis of the laser light emitted from the emission part will not tilt with respect to the optical axis of the waveguide. If the optical axis of the laser light emitted from the emission part tilts with respect to the optical axis of the waveguide, the laser light may fail to be delivered to the plasmon antenna with sufficient intensity. When the laser diode is to be arranged so that the longitudinal direction of the laser diode is perpendicular to the end face of the slider where the incident end of the waveguide is located, however, there is a problem that the longitudinal direction of the laser diode can easily tilt with respect to the direction perpendicular to the end face of the slider where the incident end of the waveguide is located, and it is thus difficult to align the laser light with the waveguide.
The laser light emitted from a laser diode may be made incident on the waveguide by other techniques. For example, as described in U.S. Patent Application Publication No. 2008/0002298 A1, the laser diode may be arranged with its emission part opposed to the surface of the slider on the trailing side so that the laser light emitted from the emission part is incident on the waveguide from above. This technique facilitates the alignment of the laser light with the waveguide.
U.S. Patent Application Publication No. 2008/0002298 A1 describes a magnetic head that includes a diffraction grating in its slider. The diffraction grating diffracts laser light that is emitted from a laser diode and enters the slider from above the slider, so that the diffracted laser light travels through the waveguide toward the medium facing surface. As a means for changing the traveling direction of the laser light, however, a mirror may be more advantageous than the diffraction grating because of its simpler structure. Providing an internal mirror in the slider is therefore conceivable, the internal mirror being intended for reflecting laser light coming from above the waveguide so that the reflected laser light travels through the waveguide toward the medium facing surface.
A method of fabricating such an internal mirror will now be discussed. In a possible method of fabricating the internal mirror, for example, an etching mask of photoresist is formed on an insulating layer of alumina or the like, and the insulating layer is taper-etched by reactive ion etching to provide the insulating layer with an inclined surface. A reflecting film of metal is then formed on the inclined surface by vapor deposition, sputtering, etc. The surface of the reflecting film serves as the reflecting surface for reflecting the laser light.
Hereinafter, a description will be given of problems that are associated with the foregoing method of fabricating the internal mirror. When taper-etching an insulating layer, the etching rate is typically lower than when etching the insulating layer perpendicularly. Given the same etching depth, an etching mask of greater thickness is therefore needed to taper-etch the insulating layer than when etching the insulating layer perpendicularly. Thicker etching masks, however, can lose their shape more easily due to plasma during etching. The foregoing method of fabricating the internal mirror therefore has the problem that it is difficult to form a plane inclined surface when fabricating an internal mirror having a reflecting surface of large dimension in the depth direction in particular, because of the deformation of the etching mask during the etching of the insulating layer for the purpose of forming the inclined surface. If the inclined surface is non-plane, the reflecting surface also becomes non-plane. This results in a drop in the amount of laser light that is reflected by the reflecting surface and travels in a desired direction, thereby causing the problem of low use efficiency of the laser light for generating near-field light.